Electromechanically-controlled switch and remote-control signaling and telephone system



Oct. 1, 1929. F. ALDENDORFF 1,730,049

ELECTROMECHANICALLY CONTROLLED SWITCH AND n uoTE CONTROL smmmuc AND TELEPHONE SYSTEM Filed Jan. 20. 1927 7 fleets-Sheet l Oct. g}, 1929. F. ALDENDORFF 7 9 ELECTROMECHANICALLY CONTROLLED SWITCH AND REMOTE CONTROL SIGNALING AND TELEPHONE SYSTEM Filed Jan. 20, 1927 7 heets-$heet 2 Oct. 1, 1929. F. ALDENDORFF 1,730,049

ELECTROMECHANICALLY CONTROLLED SWITCH AND REOTE CONTROL SIGNALING AND TELEPHONE SYSTEM I Filed Jan. 20, 1927 7 Sheets-Sheet 3 Fig.3.

Oct. 1, 1929. ALDENDQRFF 1,730,049

ELECTROMECHANICALLY CONTROLLED SWITCH AND REIOTE CONTROL SIGNALING AND TELEPHONE SYSTEM Filed Jan. 20, 1927 7 Sheets-Sheet 4 I \INIIIIIIIlllliliilllllilllllllll Fig.9., I

ELECTROMECHANICALLY QONTROLLED SWITCH AND REMOTE CONTROL SIGNALING AND TELEPHONE SYSTEM Filed Jan. 20, 1927 Y 7 Sheets-Sheet 5 O 192 F. ALDENDORFF 1,730,049

F. ALDENDORFF ELECTROMECHANICALLY CONTROLLED SWITCH AND REMOTE CONTROL SIGNALING AND TELEPHONE SYSTEM Y 7 Sheets-Sheet 7 Oct, 1, 1929.

Filed Jan. 20,1927

2 00000000000000 v0v 000000000 00 mm 000 00000 00 l Patented Oct. 1, 1929 Darren s'rA'rEs FRITZ ALDENDORFF, or BERLIN, GERMANY; CHARLOTTE ALDENDORFF HEIRESS or SAID FRITZ ALDE'NDQR'FF, DECEASED ELF.cTRoMEcHAnIoALLY-ponTnoLLEn swI'rc-H nun REMOTE-CONTROL sIGNALING AND 'rnnnrnonn SYSTEM Application filed Ianuary 20, 1927, Serial No. 162,399, and in Great Britain January 19, 1926.

This invention relates in general to electromechanically controlled systems and more particularly to telephone systems of the kind in which switches are employed whose brushes are moved by power, which may be supplied by a. spring, the brush movements being controlled by a toothed wheel attached to the brush shaft and an electromagnet armature which alternately releases and stops the wheel so that the brushes execute steps which may be of diiferent lengths. Apparatus of this character is also capable of application for mine signaling and the control of electric machinery in automatic sub-stations. So far, however, I have developed the invention particularly for telephony and this specification is mainly concerned with such developments.

In quick-acting switches of the kind referred to it is essential that the control means for starting and stopping the switches should be reliable and the more reliable the control means can be made the quicker can be the speed of operation permitted.

The present invention comprises improved means of control some of a mechanical nature and some electrical. In order to provide for accurate adjustment of the switch stopping member the pawl or braking member is made adjustable on the armature of the starting and stopping magnet. In order to avoid the necessity of restoring the potential energy of spring operated switches, an electric torque producer, such as an electric alternating current or direct current motor may be employed on each brush carrying shaft. In some cases an electrically rotated shaft may supply power to a number of switches and electric coupling means may be provided individually to each brush carrying shaft.

The improved switch of this invention, without altering the mechanical construction, may be so arranged in connection with electric operating circuits that it works as desired as line-finder, pre-selector, distributing switch with very many outlets, group selector or connector.

The new switch has on its brush spindle a wheel with teeth corresponding with the bank contacts. The wheel is driventogether with the brush spindle by a separate driving means, which may be a spring or electric motor or the like, and'is stopped at the right point by means of a pawl. The adjustment of the brushes in relation to the bank con tacts and the adjustment of the stopping pawl in relation to the teeth of the wheel issuch that the point of the pawl, at the moment when the brush ust leaves the bank contact located in front of the desired bank contact, stands in front of a tooth of the stopping wheel so that substantially the whole time whichthe brush requires to pass over the air gap separating the desired bank contact from the adjacent bank contacts is obtained for the falling in'of the stopping pawl into the correct slot between the teeth. Preferably the adjustment is suchthat the switch controlling brush to which a brush controlling magnet is connected is only stopped by the striking of a tooth of. said wheel against the stopping pawl when the narrow contacting surface of said brush has travelled at least five-sights of the distancebetween the two bank contacts between which the desired bank contact is located. Thebank contacts are embedded in a carrier or-carriers of a pressed material and these carriers can be adjusted for the purpose of'the coarse adjustment of the circle of contacts in relation to the'selector shaft. For accelerating the falling in of the stopping pawl into the wheel, a condenser reacting on the magnet winding of the control magnet-is provided which is connected preferably parallel to the magnets The retraction of the stopping magnet armature can be accelerated by making the magnetic flux path. of this magnet of nickel iron. The switch is further characterized by a control magnet, whose armature responds to absence of current at high brush speed, and a relay, which does not respond when 'the brushes connected with it pass over contacts connected to battery until the selector brushes are positively stopped by the armature of the control magnet.

In order to improve the controlling means by which the brushes of such switches are stopped at desired points of the contact bank, there are provided both at the beginning and tartar orrics; 1

middle of each long step around the contact bank with a set of indicating contacts that mark the positions where the brushes are to be arrested, and with circuit arrangements for applying potential to said sets of indicating contacts alternately in accordance with dialling impulses sent to the switch whereby the brushes are liberated so that they execute long steps, and with further circuit'arrangethe switch.

ments by which said electromagnet receives an impulse to cause it to allow the brushes to move to the last contact of a set of indicating contacts located at the beginning of a long step whenever they have been stopped on; a contact located before the last one of set at the end of a dialling operation.

According to the in-vention,the brush carrier may be driven by an electric torque producer such as an electric motor individual to The motor is stopped in a position effecting the desired connection by means of a stopping pawl, which engages in a toothed wheel connected to the brush carrier when the brushes reach a set of contacts on which it is desired that they should stop. Alternatively the brush carrier .may be stopped by means of a friction brake which comes into operation at the desired moment. At the same time or substantially so the electric supply to the motor is disconnected. The arrangement may be such that so long-as the brushes are sliding over bank contacts to which potential is not applied, the stopping pawl isheld away from the toothed wheel by means of an electromagnet which is deen-v ergized for the purpose of stopping the brushes as soon as a brush, closing the circuit of'the electromagnet, reaches a marked contact.

"Afeature of the invention consists in making thetest bank contacts. of a switch con nected to the individual lines have a longer wiping surface than the talking contacts.

The electrically driven switch, according to'the invention, can be 'operated'as a line finder, preselector, trunk finder, group selectorand connector. When used as a group selector, the hunting operation for'finding a free trunk is initiated through thecontacts of. a relay whose one winding is short-circu-ited as long as the hunting operation lasts and after a free line has been found owing to change over of contacts, the connection put through to the next switch. The arrangement is such that the hunting operation ceases in any case when the brushes have hunted over all the lines existing in the g QlP- i I When used as a connector, the switch brushes arepropelled from contact to contact by applying an electric potential to the bank contacts in succession by means ofia relay. This relay, which applies the potential alternately to different individual bank rent impulse affecting the brushes of the switch, given off by. the current impulse re: lay, originates afterthe first drop of'the ar mature and subsequent armature attraction ofthe current impulse relay. This current impulse is taken through working contacts of the current impulserelay andthe changeover relay.

()ne arrangement of electric drive comprises a motor which is. practically uncou' pled from the selectorshaft at the moment when it is started and is coupled to the se-. lector shaft after it has executed some motion, for example, half a revolution or more. At the moment when the motor is coupled a resistance or resistances are connected in the motor circuitto reduce its torque. These re sistances may be'placed in series with the motor, that is in the leads to the motor or in the armatures, windings orin any other convenient manner.

The brush shaft may be driven by a driving device associated with the switch by means of friction coupling "and positively.

stopped in the desired position by means of a locking arrangement. The driving device then appropriately consists of a separate electric torque producer associated with the switch. It may, however, also consist ofv a disc or the like secured on a continuously rotating shaft capable of being magnetized at suitable moments and a ring or the like mounted on the switch shaft which is attracted by the disc. The coupling between the torque producer or motor and the switch shaft is preferably constructed in the form of two plates drawn or pressed together which embrace aring or the like secured on the switchshaft. The switch shaft and the shaft of the driving device may be arranged parallel to one another. In another constructionalofcrm, the switch shaft and the switch of the driving device extend at right angles or at some otherangle' to one another. The switch shaft is driven with such speed that the brushes, when numerical impulses are sent by means of an impulse transmitter of the usual kind, jump between two successive current impulses always over a whole group of'contact sets and the first half of this group is jumped over at the opening of the-V-line'group and the second half of the group on the closing ofthe, line group eX- tending towards the calling subscriber. The ositive looking or stopping of the contact rushes at the desired position of the contact bank is efiected by a toothed wheel mounted on the brush carrier and a stopping pawl engaging in thetoothed wheel. 1

One feature of the invention is a power driven switch provided with a brush carrier that, when started, is driven forward until a brush reaches a waiting line and is arrested after use by a positively acting arresting member, said member being made to release the brush carrier to enable it to be driven forward again if the brush should fail to step during its first movement on a waiting line. Another feature of the invention consists in a switch provided with a spring driven brush carrying shaft, a spring rewinding shaft to which rotary motion is imparted by an electromagnetic device whose power is made effective, when the brushes of the brush carrying shaft have trailed over all of their bank contacts, by contacts closed by a member attached to the latter shaft, these contacts being opened when the brush driving spring is rewound. A further feature of the invention consists in a power driven switch whose brushes are stopped in any desired position by a positively acting electromechanically controlled member that cooperates with the brush carrier, a speed regulator being provided for regulating the speed at which the brushes pass over the bank contacts of the switch. Another feature of the invention comprises a switch having a brush carrier with an electric driving motor individual thereto, a toothed wheel that is stopped on the mechanical detent when the brushes reach a desired position and contacts for disconnecting the current supply to the motor when the brushes are stopped.

A further feature of the invention consists in a remote control switching system provided with line finders which respond in succession to effect connections with waiting lines and means by which, when a line finder fails to connect a waiting line through to a connecting line or trunk within a certain time, the waiting line causes the next idle finder to operate to connect the line to a trunk, switch or the like. Another feature of the invention comprises a remote control switching arm in which a switch is provided with a plurality of sets of selectively operable brushes mounted on one and the same brush carrier and in which there are means by which one or another set of brushes are made to effect a connection according to the first signal or series of selecting impulses sent from the calling station to the switch denotes the said one or another set of brushes. Another feature of the invention comprises an electromechanically controlled telephone system provided with a ringing cut-ofi and through-connecting relay over whose bank contacts ringing current and a relay-energizing battery are applied alternately through the brushes of a signal current switch to a wanted line. The signal current switch may be arranged sothat, when a line makes a call, current impulses are sent. from the switch at certain intervals to the operating magnet of a trunk finder for the purpose of shifting the trunk finder brushes from a faulty trunk to a-good one.

Referring to the accompanying drawings: Figure 1 is a diagrammatic perspective view of a spring driven switch which may be used with the circuits shown in Figure 2 as a line finder.

Figure 2 shows the circuits of a line finder and Figure 3 the circuits of a connector according to the invention provided with a plurality of sets of brushes- Figure 4 is a perspective view partly in sec-- tion showing the switch when spring driven. Figure 5 is a diagrammatic perspective view of a motor driven switch, Figure 6 shows a view of a switch according to the invention in which the brush. shaft is driven by a motor whose shaft extends parallel to the brush shaft. Figure 7 shows a switch in which the brush shaft extends at. right angles to the motor shaft. Figure 8 shows a switch whose brush shaft is driven by a continuously rotating driving shaft by means of friction coupling. V

Figure 9 is a front View of bank contacts and a double brush which slides over these contacts. Figure 10 is a side view of the end of a motor adjacent to the driven end of a switch, Figure 11 is a view of Figure 10 as seen from the right and Figure 12 is a circuit diagram of the motor and of parts of a switch driven by the motor. Figure 13 shows a subscribers station, two line finders working in series and four trunk finders. Figure 14 shows the circuit arrangement of a group selector and Figure 15 the circuit arrangement of a connector.

Referring now to the drawings the switch shown in Figure 1 comprises acentralbrushcarrying shaft 1 to which is fixed a toothed brush-arresting wheel 2, a worm wheel 3 and a notched disc l. Arranged to rotate around the central shaft 1 is a hollow-shaft 5 to which is fixed a spring-rewinding wheel 6, a notched disc 7, a spring box 8 and a cam 9. The spring box 8 contains a spring whose outer end is attached to'the peripheral wall of the spring box and whose inner end is fixed to the central shaft 1. Whenthe central shaft 1 is held against rotation, asby a detent 10, and the hollow-shaft 5 with the spring box 8 is rotated by the pawl of a spring-winding magnet 11 that cooperates with the wheel 6, a torque is applied to the central shaft so that when. it is released by the detent 10 being attracted by the magnet 12 the shaft 1 with the brushes 13, 14c, 15, 16 whirled round. The current through the magnet 12 flows through a hunting brush 16 and through bank contacts until the. desired set of bank contacts is reached, when the magnet. 12 is deenergized and the brushes are stopped by the detent 10 being jerked by a spring 17 into engagement with the toothed arresting wheel 2. f.

It must be noted that when the brushes 13 to 16 are in their normal position the arresting member 18 is lifted clear of the rotary stop 19 on the Wheel to allow the stop 19 to ass.

The moment the central shaft 1 is rotated out of its normal position the disc 4 closes a pair of contact springs 20 and when the hollow shaft 5 is rotated out of its normal position its disc 7 closes a pair of contact springs 21. Atthe end of a connection through the switch the central shaft is released anda projection 22 is then rotated further, i. e. in the direction of the arrow, into its home position in which it pushes a .contact spring 23 forward into contact with a sprlng 24 and thus closes, in a manner to be more fully described with reference to Figure 3, a circuit through the rewinding magnet 11 which now rotates the hollow shaft until the contacts 23, 24 are. opened through the agency of a cam 26 that turns a bell crank lever 25 which in turn raises the contact spring 23 out of the path of the projection 22 so that the latter moves forward to the front of the spring 23 as shown in Figure 1. In this position spring 23 is out of contact with spring 24 and then, or if the projection 26 is placed so as to throw the lever 25 before the hollow shaft is restored to normal, afterwards when the'contact springs 21 are opened, the re winding circuit through the magnet 11 broken. All parts of the switch have then returned to their normal position. Shortly before the hollow shaft is stopped in its normal position the cam 9 lifts the arresting member 18 out of the path of rotating stop 19 which by striking against 18 stops the central shaft 1 in its normal position in the restoring operation. The central shaft 1 is rotated at a high speed which is governed by a speed regulator whose shaft 28 is driven by the worm wheel 3 and worm 27. Attached to the shaft 28 are two springs 29, 3O loaded at their ends by weightsorfriction members 32, 33 that rub against the internal periphery of a casing 34. The degree of 'friction, and thus the speed, can be regulated by varying the resiliency of the springs 29, 30 by means of an adjustable ring 31 that can be slipped along the shaft to vary the active length of said springs.v The regulator is a considerable aid in ad" justing the switch to operate at a high speed but not too high to prevent proper stopping of the brushes 13 to 16 on any desired bank contact set. If the brushes should by any chance not be properly stopped on the bank contacts of awaiting line in their first rotation the projection 22' will close the spring contacts 23, 24 and this results in the rewinding of the brush driving spring and the unlocking of the detent 18 so that the brushes will be whirled around a second time. This time the spring power will be, small and the brush will be rotated more slowly. I

In Figure2, LF is a line finder of the type shown in Figure 1. TF is a trunk find-j er adapted to preselect a free trunk or line finder LF and to start the latter when a call is made by a line connected to the bank contacts of the line finders. In Figure 3, C is a connector with two sets vof brushes mounted on a common shaft that is rotatcd by a stepping magnet M1,. SS is a slow signal-current switch, which when a line calls, is started for the purpose of sending impulses to the trunk finder TF to shift its brushes onto another trunk in case the trunk the brushes are resting on is not connected through the waiting or calling line within a certain short time. The switch SS also intermittently connects ringing current to wanted lines. The'circuits in Figures 2 and 3 will now be more fully de scribed.

It will be assumed that a calling station (is desires a connection with a line No. 14.

When the receiver at the calling station is raised the line relay 40 is energized and at its contact 41 disconnects the positive pole from the marking contact 42 of the line finder LF. At 42 a circuit is closed through the brush 43 of the trunk finder and the finder starting relay 44. The latter relay at its contact 45 closes the circuit of the starting and stopping magnet 12 which corresponds to the magnet 12 in Figure 1. The circuit through the magnet 12 extends from the negative pole through contact 45, contact 46 of the through-connecting relay 47, brush 48, a contact similar to 42 on which the brush 48 rests in its normal position, a contact similar to contact 41 of a line relay to the positive pole. The brushes 48, 49, 50, 51, of the line finder are now whirled round'until the brush 48 reaches a contact such as 42 that is disconnected'fromthe positive pole. At this moment the'arresting pawl 10, Figure 1, stops the brushes and the relay 47 is energized byv a current flowing from the negative pole through contacts 52, 47', brush 49 contact 53 of the line relay 40, cut-off relay 54 to'the positive pole of the battery. 'The. relay 54 closes a contact 55 and thus makes the circuit through itself and through the relay 47 independent of the contact 53 which is opened when the relay 54 is energized, because here 1 by the line relay 40 is disconnected and de energized, The relay 47 connects the calling line through contacts 56, 57 .to the impulse relay 100 of the connector G and this relay is then energized by current flowing to the Waiting station. At its contact 101the impulse relay closes a circuit for the release relay 102, which circuit extends from the negative pole through 102, resistance 103, to the positive pole. The moment the release relay 102 is energized, it establishes a locking circuit for itself at contacts 104, a new circuit for the relay 47 at contact 105 and a shifting circuit for the trunk finder TF at contact 106. The magnet 60 of the trunk finder is then energized by current flowing through its bank contacts 61, brush 62, 60 to the negative interrupter. The brushes 43, 62, 63 of the trunk finder are now stepped down until the brush 62 reaches a contact like 61 that is not connected through a contact like 106 to the positive pole.

The described operation of connecting a calling line through the line finder to the impulse relay 100 associated with its trunk should normally take place in a fraction of a second. If this through-connecting operation is not executed within a certain time after the energization of the line relay 40, the brushes of the trunk finder TF will be shifted to another trunk by a safety device that comprises relays 64, 65 and certain con tacts on the slowly stepping signaling switch SS. When the relay 64 is energized it closes a circuit that extends from the negative pole through 69, oscillating member St of a slow-acting interrupter, winding 107 of the slow interrupter to the positive pole. The slow interrupter has an armature 108 which on its attraction by the winding 107 fiings round the arm 109, this arm 109 is caused to swing back rather slowly to re-establish a contact at 111. By this means slowly recurring impulses are sent through the stepping magnet 112 of the signal switch which steps its brushes 113, 114, 115, 116 from contact set to contact set. When the brush 116 reaches the bank contact 117, the relay 65 is energized and closes a lockingcin cuit for itself at its contact 118. When the brush 116 reaches contact 119 a currentimpulse is sent to the operating magnet 60 of the trunk finder in a circuit which extends from the positive pole through 118,'brush' 116, contact 119, wire 121, contact 122, brush 63, magnet 60 to the negative pole. The magnet 60 then steps the brushes of the trunk finder onto the bank contact set of another trunk and an impulse then flows from the positive pole through contact 42, brush 43 of the trunk finder to a starting relay like 44 of the next idle trunk. This causes the line finder of that particular trunk" to be started and to connect the waiting line to an idle trunk or link. The moment the waiting line is connected through the line relay 40 is deenergized and this in turn causes the deenergization of the relays 64 and 65 and also the stoppage of the signal switch SS. If a trunk belonging to a bank contact or 72 of thetrunk finder is faulty an impulse will within a certain period be sent from the signal switch SS over wire 123, cont-act 124 or 125, brush 63 to the magnet 60 of the trunk finder to step the latter on to another trunk. v

If, during its first rotation the line finder should operate at too high a speed to enable the arresting pawl of the arresting magnet 12 to stop the brushes on the proper line, the

projection 22 attached to the disc 4, (see also Figure 1,) will be whirled completely around and will press the contact spring 23 against spring 24 so as to close the circuit of the rewinding magnet 11.

lay 81 is energized and at contact 82 shortcircuits itself and thus causes the magnet 11 to respond. Immediately afterwards the relay 81 allows its armature to drop back so as to weaken the current in the rewinding magnet 11 sufiiciently to cause it to deenergize. The oscillations of the armature of the relay 81 thus cause stepping impulses to flow through the rewinding magnet 11. The'magnet 11 steps the hollow shaft and the notched disc 7 around and after it has turned through a certain angle a projection 26 attached .to it causes the contacts 23, 24 to be opened. The cam 9 on the hollow shaft raises the detent 18 been connected through to the impulse relay 100 and that the release relay 102 has been energized as described, the slow interrupter SI will be started by a circuit extending from the negative pole through contact 104, contact 130, 109, 111, 107 to the positive pole. The

This circuit extends from the positive pole through 11, 24, 23, wire '80, winding 81 to the negative pole. The resignal switch SS is thus started for the purpose of sending out ringing current at the proper moment that is when the brushes of the connector C have been stepped on to a wanted idle line. The calling station now terruption of the current in the impulse relay 100 and a stepping impulse flows from the negative pole through contact 104, contact 131 of impulse relay, stepping magnet M to the positive pole. A pause now ensues before the unit selecting impulses aresent and during this pause the changeover relay 132 which was energized when the armature of the impulse relay dropped back and opened works the dial and thus gives rise to one in- "the short-circuit of the relay 132, closes at its 'cam 135 to close the contact 134. If two tens impulses are sent through the impulse relay 100, the cam 135 will pass beyond the contact springs 134 and a change-over action that takes place after the tens impulses have been sent in will then fail to close a circuit through 133, 134and the brush-changing relay 136 so that the brushes 137, 138, 139 will remain connected to the trunk instead of the brushes 140, 141, 142 being connected thereto.

Assuming that the brush-changing relay 136 has been energized as described, this relay closes at its contact 143 a locking circuit for itself that extends through contact 104 to the negative pole. When the units impulses are now sent in the stepping magnet M receives impulses as before in a circuit extending from the negative pole through 105, contact 131, magnet M to the positive pole. This steps the brushes 140, 141, 142 on to the bank contacts of line 14. When the units impulses cease, the change-over relay 132 allows its armature to drop back and, if the wanted line is free, the test relay is now energized in a circuit extending from the negative pole through 104, contact 133, test relay 150, contact 151, test brush 142, test wire 151, contact like 152 on the line relay of the wanted line, cut-off relay like 54 to the positive pole.

When the test relay is thus energized it shortcircuits a part of its windingthrough contact 154 andthus reduces the potential on the multiple test bank contacts of the connectors so as to render the wanted line busy. At its contacts 155, 156 a circuit is now closed for intermittent ringing current which flows through brushes 113, 114, wires 157, 158, contacts 159, 160 on athroughbonnecting and ringing cut off relay 161. In the intervals between the ringing current impulses, a negative battery pole is connected by brush 115 to the wire 162 and through this wire and contact 163 to the lower winding ofthe relay 161. When the wanted subscriber responds continuous current flows through the windings of the relay 161 and this relay is then energized to close contacts 164 and 165, 166, 167. The relay 161 looks itself through contact 166 until a wanted subscriber replaces his receiver. At contact 167, the relay 161 closes the circuit of an auxiliary release relay 168 which latter relay opens the circuit of the slowinterrupter at contact 130 and closes a locking circuit for itself at contact 169.

When the wanted subscriber replaces his receiver, the connector C is restored to normal by impulses that flow through the magnet in a circuit extending from the positive pole through M contact 171, contact 172, contact 173 to the impulser 81. Vhen the brushes reach their normal position, this restoring circuit is opened by the off-normal contact 173. When the calling subscriber replaces his receiver the circuit of the relay 47 which produces the busy condition of the calling line is opened at contact 105 and at contact 46 the magnet 12 of line finder is then energized in a circuit extending from the negative pole through 12, contacts 20, contact 46, brush 48, contact 42, contact 41 of the line relay to the positive pole. The arresting detent is thus disengaged from the arresting wheel, see Figure 1, of the brush carrying shaft and this shaft is restored to its normal position until the projection 22 pushes the;....

tacts 173 to the impulser 81.

Referring now to Figure 4, the switch has a shaft 1 on which the brushes are secured in an insulated manner, only the brush 2 being shown. In the shaft 1, mounted to rotate thereon, is a hollow shaft 5 which carries at its upper end a gear wheel 6 and at the lower end a spring-box 7. The one end of the spring 8 is connected with the shaft 1 and the other end with the casing of the spring- 'box 7, so that when the spring box is rotated in the direction of the arrow, the spring 8 tends also to'rotate the brush shaft in the same direction. The rotation of the spring box and consequently also the tensioning of the spring is effected by means of a propelling pawl 10, which is made to vibrate by an -electromagnet 5 which rotates step-by-step a toothed wheel 6 connected with the spring box. Return rotations of the wheel 6 are prevented by a locking pawl 9. Thebrush shaft 1 is held against the action of the spring 8 by means of a stopping pawl 4 which engages in the teeth of a wheel 3 secured on the shaft 1. In order to stop the brushes 12 on any bank contact the stopping pawl 4 is lifted out of the wheel 3 by excitation of the control magnet 11 and as soon as the brush leaves the bank contact located in front of the desired bank contact the magnet 11 is again deenergized so that the pawl again engages the wheel 3 and stops it. The exciting currentof the magnetll flows through the brush 12 and the bank contacts wiped by it. All the bank contacts except, for example, 15, where the brush is to stop, are connected with the battery. The adjust-ment of the brush 12 in relation to the bank contacts and the adjustment of the stopping pawl 4 in relation to the teeth of the wheel 3, the stopping pawl being adjustable on the armature lever 20, is such "ice that the point of the pawl 4 at the moment when the brush 12 just leaves the bank contact 14 lying in front of the desired bank contact 15, stands in front of a tip of a. tooth of the locking wheel 3 so that the entire time which the brush 12 needs in order to pass over to the desired bank contact 15 and over the air gap 17 separating the adjacent bank contacts 14, 15 is obtained for the falling of the stopping pawl 4 into the correct tooth gap. The slotted pawl 4 is screwed fast by screws 4 on the armature lever 20 and secured against displacement by means of a screw 4" adjustable in a screw-threaded aperture of the bent up end of the armature lever 20. Appropriately also a security nut is provided. The time of dropping in of the pawl 4 can be adjusted by regulation of the tension of the armature return spring 19. An important means for shortening the time of falling of the armature 20 and for the rapid engagement of the stopping pawl 4 in the correct tooth gap, is the condenser C reacting on the magnet coil 11, the condenser may be connected parallel to the coil 11. By means of the condenser C the result is obtained that the current in the coil 11 when its circuit is opened not only closes more quickly but to a certain extent reverses its direction. By this means the residual magnetism of the control. magnet core is opposed. It has been found in practice that the selector will stop its brushes with sufiicient certainty when it wipes over its bank contacts with a speed of 300 contacts per second. A 100 point linefinder of this construction, therefore, reaches the hundredth bank contact lying furthest away from the normal position of the brushes in one third of a second so that the use of a dialling tone which indicates to a calling subscriber that his line is connected to the next selector and consequently he can operate his dial is dispensed with.

The switch shown in Figure 5, has a brush carrier or a brush shaft 1 on which the brushes 2, 3, 4, 5 are secured in an insulated manner. The shaft also carries a toothed wheel 6, the armature 7 of an electric torque producer or electric motor 9' and a worm wheel 8 which engages in a worm of a speed regulator 10".

The operation of the switch is such that as soon as the brushes are to be set on any particular contact or shortly beforehand, the electric motor 9 is switched in and then the magnet 11 withdraws the stopping pawl 12 from the stopping wheel 6. The brush carrier 1 is whirled round with high speed, which is regulated by regulator 10, until the test brush 5 reaches the one dead test contact, for example, 13, when the circuit of the electromagnet 11 is broken. The electromagnet 11 is then rapidly deenergized and the stopping pawl 12 falls into engagethe brush carrier 1 fast. Simultaneously or shortly thereafter, the electric motor 9"is disconnected. In order to obtain an exact operation of the stopping pawl 12, the test bank contacts 13 are made longer than the wheel 6 in which the stopping pawl of the armature 12 of a magnet 11 engages. On the wheel 6 is secured a ring 4 which has a ring surface 5 extending inwards. The ring surface 5 is embraced by two plates 7, 8 pressed against one another which constitute the driving wheel of an electricmotor 9. When the switch is set into operation, the motor 9 is switched in and simultaneously or a little later, the electromagnet 11 is excited which then lifts the stopping pawl 6 out of the stopping wheel 6 and liberates the brush shaft 1. The magnet 11 is kept excited by a current which flows through the brush 5 and bank contacts 13 until a contact 13 is reached which is disconnected from battery. At that moment the current through the electromagnet 11 and the brush 5 is interrupted and the armature 12 is brought back into its normal. position by a spring when the stopping pawl engages in the stopping wheel 6 and thereby stops the brush shaft. The brush 5 is constructed as a double brush and in the passage of the brush from one bank contact 13 to-the next, the one brush half 5 leaves the next contact 13 before the other brush half 5 leaves the preceding bank contact 13. This feature, of course, is also applicable to the spring driven switch. The adjustment of the stopping pawl is such that thebrush 5 has always wiped over the greatest part of a bank contact 13 before the corresponding teeth of the stopping wheel 6 abuts against the stopping pawl. By this means the greatest possible time of falling for the armature 12 of the switch is obtained.

The details of the switch shown in Figure 12 corresponds to those of Figures 11,14 and 15 with the exception that the motor shaft extends at a right angle to'the brush shaft. If necessary, the motor and brush shaft may be at angle to one another other than a right angle. plates 7', 8 which are pressed against one another by the nut, embrace a ring 4 projecting downwards secured on the stopping wheel 6 and thereby driving the brush shaft.

meat with the stopping wheel 6 and holds In the switch shown in Figure 13, the

In Figure 12 the two elastic brush shaft 1 is provided with an elastic disc 12 which carries an iron ring 4 On continuously rotating shaft 11, is secured an iron disc 7Twhich for the purpose of setting r the switch into operation is magnetized by a coil 9. When the disc 7 is magnetized or immediately thereafter, the starting and stopping magnet 11 is excited and the disc 7 a then drives the brush shaft 1 by means of the ring 4*. The brush shaft may be provided with a speed regulator like in Figure 10.

In Figure 16 a represents a fragment of the motor field magnet which is built up of thin 15 iron sheets. 6 is afield winding and 0 is a bearing in which the motor shaft (Z that carries a disc 6 is journalled. Projecting from the disc 6 is a pin 7 and a finger g. Fixed on the disc 6 are also resistances 71,71 and contact springs j, Z and m, Protruding through the 16 only, turns the disc 6 and the armature of the motor so that the pin f rests against the top end of the carrier arm 0. When the motor is switched on, its armature turns its shaft 03 and its disc 6 in the direction of the arrow and '30 the only mechanical resistance that the armature has to overcome initially is that of the weak spring ;0. After the armature has executed slightly more than half a revolution, the stud 0 and immediately thereafter, the

1 finger g strikes against the upper end of the arm 0 and commences rotating the shaft 1 of the switch. The stud 0 is forced back in the hole in finger g and the contacts j, Z and and m, n are opened, whereby resistances h, i are inserted in the armature winding and the torque of the armature is reduced, (see Figure 18) in which 11 represents the controlling magnet of the switch driven by the motor, 5 is the selector brush that cooperates with the stopping magnet 11. 13 are bank contacts and 12 thestopping pawl which cooperates with the brush stopping wheel 6. C is a condenser which is connected in parallel with the brush 5 It accelerates the dropping back 5 of the armature 12 of the selector controlling magnet 11 when the brush 5 reaches a bank contact, which is devoid of potential.

The resistance or resistances 7nd could be laced outside the motor, but then it would e necessary to arrange slip contact rings and corresponding brushes on the motor or selector shaft. With the arrangement shown in Figures 16 and 17, the blow delivered against the stud 0 when it strikes against the carrier arm 0 results in a sudden and wide opening of the contacts j, Z and m, n and this reduces sparking atthese contacts.

Referring to Figures 19 to 21, the circuit operations will now be explained which take place in making a connection with wanted subscriber N0. 223. When the calling subscriber S takes down his receiver from thehook, a current flows from the positive pole through the line relay 20, contact 21 of the cut-off relay 22, telephone instrument S, contact 22 of the cut-off relay 23 to the negative pole. The relay 20 connects by means of the contact 24, the cut-off relay 23 with the bank contact 25 of a first line finder LF at the contact 26 it closes through a resistance 27, the circuit of a stepping relay 28 and at the contact 29 it cuts off the positive pole from the marking bank contact 30. The stepping relay receives through the resistance 27, sufiicient current to close its contacts 31, 32 whilst the contacts 33, 34 are only closed when a second subscriber calls and connects the positive pole through the corresponding line relay 35 and a further resistance 36 with the starting line 37 Through the closure, of the contact 31, the first line finder LF 'is started and through the closure of the contact 32, the second line finder LF is started in connection with which it should be observed that the trunk finders TF and TF have already set their brushes previously on free trunks in. manner to be described later.

The starting magnet 11 of the line finder LF receives current which flows from the negative pole through 11 contact 38, line 39, brush 40, contact 31, brush 42, a contact corresponding to the contact 29 of a non-calling subscriber or other subscriber to the positive pole. The stopping magnet 11 closes at its contact 43 a circuit independent of the contacts 38 and 31; at the contact 44 it prepares a circuit for the through-connecting relay 45. At the contact 46 it closes an exciting circuit for a relay 47 and at the contact 48 it switches in the motor 9. Since the magnet 11 simultaneously draws out the stopping pawl from the stopping wheel (see 6, Figure 10) the motor 9 now whirls the brushes 42, 49, 50, 51 round with high speed until the brush 42 reaches contact 30 through which the positive pole is disconnected. At this moment, the magnet 11 is deprived of current, the stopping pawl falls into engagement with the stopping wheel. and holds the brushes 42, 49, 50, 51 fast. At the contact 49 the circuit of the magnet 11 is again interrupted whilst at the contacts 46, 48, the slow-acting relay 47 and the motor 9 are disconnected. Through the contact 44 of, the slowdropping relay 4?, however, the through-connecting relay 45 is excited in a circuit which extends from the negative pole through 44, 45, 49, 25, 24, cut-off relay 23 to the positive pole. Relay 45 connects the brushes 51, 50 through the contacts 52, 53 to the bank contacts of the second line finder LF". After its excitation the relay 45 also receives current through the upper low rewhich has in the meantime responded to the positive pole. By means of the circuit just described, the potential on the test line 57 leading to the connectors is lowered to such an extent that the calling line continues to appear engaged. The relay 47 at the contact 58 cuts off the positive pole from the marking contact 101 of the second line finder LF and at the contact 59 it closes a circuit for the test relay 60 and the driving magnet 61 of the trunk finder TF The magnet 61 is excited by current impulses which extend from the negative pole through 59, brushes 62, 61, interrupter 63 to the positive pole. So long as the brushes of the trunk finder TF reach engaged trunks, the magnet 61 receives negative impulses through contacts which correspond to the contact 59 of a relay 47 or the contact 64 of a relay 45 so that the brushes are continuously carried through. Furthermore, so long as the brushes of the trunk finder reach lines which are already engaged by another trunk finder, the magnet 61 receives negative impulses which extend through acontact 66, brush 68 of another finder, 67, brush 65, contact 68, magnet 61, interrupter 63 to the positive pole. So soon, however, as the brushes of the trunk finder TF reach a line which is not engaged and is not taken by another trunk finder, the circuit of the magnet 61 and of the relay 60 is broken and the brushes remain stationary on the particular trunk. The contact 69 of the relay 60 then marks the trunk reached as engaged so that another trunk finder will not remain on this line.

If the second line finder LF does not already stand on the trunk belonging to the line finder LF its starting magnet 112 is excited by a current which flows from the negative pole through 112, line 102, line 119, brush 104, contact 32 of the stepping relay 28, brush 105, line 106, 107, brush 108, contact like 101, a contact like 58, which at this moment is closed, to the positive pole, The magnet 112 closes at the contact 113, the circuit of the motor 19 and at the contact 114 it closes an exciting circuit for a relay 115 at which contact 116 engages in a starting magnet 117 in the trunk finder TF (negative pole, 116, 118, 103, brush 121, 117, positive pole). The starting magnet 117 closes at the contact 122, the circuit of the motor 19 and this now moves the brushes of the trunk finder until the brush 121 reaches a disconnected trunk, that is to say, a trunk whose line 118 is not connected with the negative pole. The magnet 117 also remains excited until the brush 123 of the trunk finder TF reaches a line which is not already connected by other trunk finders. The test lines 124 of these connected lines are connected by contacts 125 with the negative pole and an excited magnet 117 will therefore receive cur rent through its contacts 126 over those lines 124 connected with the negative pole. As

soon, however, as the brush 123 reaches a disconnected line, the armature of the magnet 11-7 falls oft and the stopping pawl falls into engagement in the gear wheel of the trunk finder Tl? and holds the brush fast. At the same time, the motor 19 is cut out at the contact 122.

The starting magnet'112 of the second lin finder TF excited in the above described manner, provides for itself at contact 128, a circuit independent of the contact 32 of the stepping relay 28 which extends through the brush 108 and test contacts which are connected through contacts like 58 with the positive pole. As soon as the brush 108 reaches the test contact 101, which is disconnected atthe contact 58 from the positive pole, the magnet 112 lets its armature fall off, discon nects at contact 113, the motor 19, opens at contact 114 the circuit of the left exciting winding of the relay 115 and interrupts at a second position its own circuit at the contact 128. The relay 115 lets its armature fallback slowly and there arises'therefore an exciting circuit for the relay 130 which extends from the negative pole through 116, 130, 129 to the positive pole. The relay 130 now therefore connects the brushes 133, 134 to the group selector or tothe current impulse relay 135 and this relay now receives current which extends from the positive pole through the left winding of 135, contact 136,131, 133, 52, 51, calling station S, 50, 52, 134, 132, 137, right relay 135 to the negative pole. I The relay 135 at its contact 138, closes an exciting circuit independent of the contact 116 through the right winding of the release relay 115 and through the resistance 139.

At the moment when the relay 130 is ex cited, the upper winding of the relay 47 is short-circuited since the negative pole is directly applied at the contact 54 through the contacts 116, 140, brush 141. The relay 47 then lets its armature fall 06; and the relay 45 now remains excited by means of a current 2 which flows from the negative pole through 146, 140, 141, 55, through the low resistance winding of 45.

From the above description, it is clear that the first and second line finders LF and LF are started at the same time through a pair of trunk finders TF and TF and that after this starting operation the trunk finders imers. The described operation of connecting. the calling line through. 200-p0int line finders, in every case on account of the high working speed of the line finder,takes place in a small fraction of asecond. After its connecting through, a current impulse relay 35 of a group selectorGF is excited in the manner described. It was assumed that the cal-ling subscriber desires the number 223. He will, therefore, now operate his dial so that two in terruptions of the current flowing through the current impulse relay 135 are caused. At the first interruption, a contact 143 of a shortcircuit bridgingthe change-over relay 144 is removed, so that this relay is excited by a current extending from the negative pole 116, 144, resistance 145 tothe positive pole and opens a contact 146 and closes a second contact 147 for the purpose of preparing. a circuit for the control magnet 111 When the current closing relay 135 now again attracts its armature, it closes at the contact 1g48, a circuit extending through the magnet 111 whichex tends from the negative pole through 148', line 149, bank contact150, brush 151, contact 147, magnet 111 which corresponds to the magnet 11 (Figure 10) to the positive pole.. The motor 109 was already previously connected in through the contact 155 of'the relay 115 and as soon as the magnet 111 is excited in the manner described, the motor now drives the brushes over the bank contact until the brush 151 reaches a contact 156 which is not connected with the negative pole. Here the magnet 111 is deenergized and the stopping pawl controlled by it released to engage in the stopping wheel. The brushes, therefore, remain stationary until anegative potential is con nected with the contact 156. This takes place on the occasion of the armature drop of relay 135 which is caused by the second line interruption of the sending of numerical impulses which extends from the negative pole through 157, contact 156, brush 151, contact 147, 111 to the positive pole. The stopping pawl now again liberates the brush until the brush 151 reaches the contact 158 which is not connected with the negative pole. On the subsequent armature attraction of relay 135, the magnet 111 receives a further current which extends from the negative pole, 148,. 158,144, 111 to the positive pole. The brushes151 to 154 are now released until the brush 151 reaches the contact 159., The brushes are now set on the beginning of the second group of contact sets which lead to the connectors of the second group and'there now ensues a pause in the sending of numerical impulses until the change-over relay 144 at contact 143 is c'on-' tinuously short-circuite'd and is thereby caused to let, its armature fall back in order to close at contact146 a circuit for a slow falling off relay 17 0 which extends from the negative pole through a resistance 171, 146, shaft contact 161, 170 to the positive pole.

The relay 170 connects in at contact 172, the

lower winding of the stepping relay 162 and the latter now closes its contacts 173, 174, 164, 175. Owing to excitation of the two relays 162, 170, the magnet 111 is connected through the shaft contact 169, contact 176 of the relay 170, contact 164 of the relay 162 with the brush 152 and in the case that the brush stands on a closing contact 160 connected with the negative pole, that is to say, on the test contact of an engaged line, the excitation of the magnet 111 now takes place and this magnet applies itself through its contact 167, shunting the contacts 169, 17 6 direct on the line 168 which leads through the contact 164 to the brush 152. The brushes are again released and wipe over the contact sets until the brush 152 reaches a contact, for example, 166, which has no connection with the negative pole. The current is then interrupted by means of the magnet 111 and the upper winding of the stepping relay 162, which only then was short-circuited at contact 167, receives owing to the removal of this short-circuit, a current which flows from the negative pole through contact 201 of the release relay 203 of the connector, contact 166, brush152, contact 174, upper winding of relay 162, winding 111 to the positive pole. In this circuit, the magnet 111 is not excited on account ofthe high resistance of the upper winding of the relay 162. However, the upper winding of the relay 162 opens contacts 178,- 136, 137 and at the same time connects the talking line 179, 180 to the brushes 153, 154 and to the current impulse relay 204 of the connector FS. It should be observed that at the moment of deenergization of the starting and stopping magnet 111 the brushes 153, 154 for the purpose of exciting the current impulse relay 204, are bridged over temporarily by a shunt path which extends from the brush 154 through contact 181 of the magnet 111 contact 175 of the relay 162, contact 178 of the relay 162, contact 182 of the relay 170 to the relay 3. This shunt path was closed at the moment when the contact of the mag net 111 was opened and thus made thelower winding of relay 17 0 dead. In case after selecting the group, the brushes 151, 154 already stand on a free trunk, that is to say, without hunting operation, there takes place through the closure of the path extending from the magnet 111 through contacts 169, 176, 164, brush 152, no excitation of the magnet 111 and consequently no excitation of the lower winding of relay 17 0 through the contact 183 of the electromagnet 111 The upper winding of relay 170 is short-circuited by closure of the contact 173 of the relay 162 so that the relay 17 O lets its armature again fall ofl' and at contact 182 temporarily bridges over the brushes 153. 154 through a path which extends from the brush 154 through contacts 181, 175, 178, 182 to the brush 153.

By this means the current impulse relay 204 of the group selector is excited and thus interrupts at contact 205, the circuit of the release relay 203 which extends from the negative pole through 205, 203, resistance 206 to the positive pole. The relay 203 closes a contact 201 and a current then flows through the upper winding of the stepping relay 162 in the group selector which flows from the negative aole through 201, test line 207, test contact, test brush 152, contact 17 4, upper winding of relay 162, winding of electromagnet 111 to the positive pole. On account of the high resistance of the upper winding of relay 162 this relay only is effected, not however, the

electromagnet 111 The relay 162 opens at contact 17 8, the above described bridge for the brushes 153, 154 and connects the calling line through to the contacts 185, 186 to the current impulse relay 204. The current impulse relay 138 is cut 0E at the contacts 136, 137 so that the relays 115, 144 are deenergized. The dissolution of the connection which would otherwise take place on account of the deenergization of the release relay 115, is however, prevented by the contact 175 of the stepping relay 162 which holds the through connecting relay 130 excited by means of a current which extends from the negative pole through 1.75 130,129 to the positive pole. The calling subscriber is now connected with the connector or final selector FS and since he wishes to make a connection with the second tens group, he'causes by his dial two interruptions of the current flowing through the relay 204. At the first interruption, a short-circuit bridging'over the relay 209 is opened at contact 208 so that this relay is excited by a current extending from the negative pol.ethrough contact 201, relay 209, resistance 210 to the positive pole,

On the subsequent attraction of the armature of the relay 204, the magnet 211 which corresponds to the magnet 11, Figure 1, receives a current impulse which. flows from the negative pole 212, relay contact 213, bank contact 214, brush 215, contact 216, magnet 211 to the positive pole. Through this the stopping pawl is withdrawn from the stopping wheel of the brush carrier and the motor209 which was already previously switched in through the contact- 217 of the release relay 203, now whirls the brushes 215, 216, 217, 218, 219 further up to a'contact 220 which has no con nection with the negative pole. On the next interruption which is caused by the impulse transmitter, the control magnet'211 receives a current impulse which flows from the negative pole through 201, 224, contact 225, bank contact 220, brush215, armature 2160f the relay 226, 211 to thepositive pole and the brushes are now rotated further until they reach the contact221which is in connection with the negative pole. 'At this moment the through 205, 208, contact relay control magnet 211 allows the stopping pawl to catch in the stopping wheel so that the brushes are held. On the closing of the line atthe numerical switch falling on the line interruption, the magnet 211 receives a tur- (her current impulse which flows from the negative pole through 210, 208, 212, 213, bank contact 221, brush 215, contact 216, 211 to the positive poleand the brushes 215 to 219 are now driven further by the motor until the brush 215 reaches the next intermediate contact 223 not connected with the negative pole. The brushes are now set on the second tens group and a pause ensues in the sending otnumerical impulses in which the relay '209 closes at the contact 228 a circuit for the receiving relay 226 which extends from the negative pole through 228, 229, of the shaft switch, upper winding of relay 226 to the positive pole. Relay 226 is excited and closes at contact 230 a circuit for'iteelf which extends through contact 231 and 201 to the negative pole. The lines leading from the current impulse relay 204 to the control bank contacts for the group selector, are opened at the contacts 213, 225 and the units line 232 is connected through contact 233 with a. relay 234. When the calling subscriber now sends in the three numerical current impulses, the iirst control current impulse flows from the negative pole through contact 201, 224, 232, 233, winding of relay 234, line 235,

contact 236, brush 216, contact 237 which was closed b the excitation of the relay 226, magnet 211 to the. positive pole. Therelay 234 short-circuits its lower winding and then a current flows through the contact 238 which excites the magnet 211. The brushes are hereby caused to move'to the next switch contact set where the brush 216 rests on the bank contact set, 240. As soon now as the armature of the relay 204 is attracted and thus opens the contact 224, the. relay 234 is deenergized by opening of the holding winding of this relay at contact 241' on the second interruption otthe line and closure of the contact 224 caused by the numerical switch the control magnet 211 is excited by a current which extends from the negative pole, through 201, 224,233, lower winding of relay 234, control contact 250, brush 216, contact 237, magnet 211 to the positive pole. The excitation takes place immediately the lower winding of the relay 234 isshort-circuited at contact 238 and the brushes now travel to the contact set on which the desired line number 223 is connected.

During'the sending of units current impulses, the contact 251 of the change-over 209 isclosed and a relay 253 is inserted at contact 252 which prepares a test circuit for the relay-254 at contact 255 and at cona continued short-circuit through the contact 208 and the negative pole is connected through contact 228, contact 255 of the slowly falling off relay 253 to the test relay 254. If the desired line is free, the test relay 254 is excited by a current flowing through the brush 217, test line 260 which corresponds to a test line 260, Figure 2, cut-off relay of the desired line which corresponds to the cutoff relay 23, Figure 2, and the test relay opens at contact 251 the engaged signal circuit, at 263 short-circuits a partof its winding for the purpose of making the desired line engaged, connects by the contacts 264, 265 the talking lines 266, 267 to the desired line and closes at contact 268 the circuit of a ringing current relay 269 which is now excited by current interruptions flowing through the interrupter 270 at predetermined time intervals. At the first moment a ringing current flows from the ringing current machine 272 through resistance 273, contact 274, contact 275, 265, brush 219, to the desired subscriber station and then back through the brush 218, contact 265, line 267, lower relay winding of a relay 276 to earth. The wanted subscriber now receives ringing current impulses until he takes down his receiver. There flows then either an amplified alternating current from the ringing current machine 272 or from the exchange battery 278, through contact 279, through the call station and through the lower winding of relay 27 6 and this relay is then excited. At the contact 231 the relay 276 opens the holding circuit of the relay 226; at the contacts 279, 280 it makes the talking current circuit between the calling and called subscribers and at contact 275 it disconnects the ringing current machine from the wanted line.

The subscribers can now carry on their conversation. If the called subscriber hangs up his receiver at the end of the conversation, the relay 27 6 is again deenergized and at contact 282 a short-circuit is made bridging over the release relay 203 which extends fromthe positive pole through contact 283 of the shaft switch 28 4, contact 285 of the relay 226, contact 280. The release relay 203 lets its armature fall back and closes at contact 286, a circuit for the control magnet 211 which extends through the contact 287. Through the contacts 286, 288 at the same time, the. motor 209 is switched in. The control magnet 211 withdraws the stopping pawl from the toothed wheel in order to release the brushes and these are now rotated by the motor 209 into the normal position Where they are again stopped by deenergization of the control magnet 211. The deenergization of the-control magnet 211 is effected by the fact that the cam disc 290 on the switch shaft, on reaching the normal position of the brushes, lets the spring of contact 287 or the spring of contact 288 fall into a notch. By this opennet 111 ing of the contacts 287, 288 the control magnet and the motor 209 are deenergized. The maintaining circuit of the relay 253 was already interrupted on the excitation of the test relay 254 at contact 262. The test relay 254 at the end of the connection loses its current through the opening of the contact 201 of the release relay 203. The contacts 283, 229 of the shaft switch 284, are opened as soon as the switch shaft comes back into its normal position. All parts of the connector FS as far as the current impulse relay 204, have now returned to their position of rest. When the calling subscriber hangs up his receiver, the release relay 203 is short-circuited on a path independent of the already described short-circuit path. In case the called subscriber has not yet hung up his receiver, by this means the release or the return of the connector into the normal position takes place in the manner already described.

' The return of the group selector GS is initiated by the going off of the negative pole from the line 207 at the contact 201. By this means the current flowing through the top Winding of the relay 174 is interrupted so that this relay dies down and closes its contacts 178, 136, 137, 190 controlled in its second switching stage. Through the contact 190 the control magnet 111 is inserted in acircuit which extends from the negative pole through contact 191 of the release relay 115, cam disc contact 192, 190, 111 to the positive pole. The control magnet 111 connects in at contact 194, the motor 109 which now turns the brushes of the group selector .into the normal position. As soon as this normal position is reached the spring of contact 291 falls into a notch of cam disc 195, whereby the circuit of the control magnet 111 is opened and hereby the stopping pawl of the selectoris caused to engage in the toothed wheel of the brush shaft and to stop it. By the deenergization of the magnet 111 at the same time the motor 109 is disconnected at the contact 194. The relay 174 removes at contact 17 5 the short-circuit of the right winding of relay 170 and this relay is then again excited by a current flowing from the positive pole through 171, 146, 161. The left winding of the relay 170 also receives during the returning of the brushes or during the further movement of the same into the normal position, a current flowing through the contact 183 of the control mag- During the contact 172 of the relay 170, the lower winding of the relay 174 is inserted and by this means the contact 17 5 of the first switching stage of the relay 174 is closed. As soon, however, as the group selector reaches its normal position, the left winding of the relay 170 is disconnected at the contact 183 and since the right winding of the relay 170 is short-circuited by the contact 17 5 the relay 17 0 lets its armature fall ofi whereby the lower winding of the relay 174 is finally disconnected. The negative pole is thereby disconnected "from the relay 130 of the second line-finder LF and the relay of the first line-finder LF These relays now let their armatures fall off. The brushes of the first and second linefinders remain in the positions they have taken up until they are again moved for the purpose of making connections through other bank contacts. They can even make new connections without moving their brushes.

In case the called line after the setting of the brushes of the connector is found engaged, a current flows from the engaged tone device 263, through contacts 298, 261, 256, winding 297 of the current impulse relay 204- and by this means there are produced in the coils of the relay 204:, busy tones which indicate to the calling subscriber that the wanted line is engaged. The calling subscriber then hangs up his receiver and thus causes the short-circuiting of the release relay 203 and thus initiates the already described operation for the dissolution of the connection.

1. In a telephone system, a plurality of telephone lines, a plurality of bank contacts in which said lines terminate, brushes for wiping over said bank contacts, means controlled over one of said lines for causing said brushes to move at a high rate of speed to seize said line, and means effective when said brushes fail to seize the said line during a first attempt for causing said brushes to make a second attempt to seize said line but at a lower rate of speed.

2. In a telephone system, a plurality of telephone lines, a plurality of bank contacts in which said lines terminate, a brush set for wiping over said contacts, a spring normally tensioned and tending to drive said brushes over said bank contacts, means controlled over one of said lines for releasing said brushes to seize said one of said lines, means effective when said brushes accidentally pass by said line for causing said spring to be retensioned but to a lower degree whereby said brushes are caused to make a second attempt to seize the calling line at a lower rate of speed.

3. In a telephone system, a plurality of bank contacts in which said lines terminate, means for designating a particular set of bank contacts, a set of brushes for wiping over said contacts, means for driving said brushes until said designated contact set is reached, means for arresting said brushes on said designated set, and means effective when said brushes fail to be so arrested for releasing said arresting means to cause said bruhes to be again moved at a different rate of speed in a second attempt to stop on said designated set.

l. In a telephone system, a plurality of telephone lines, a plurality of bank contacts in which .said lines terminate, brushes for wiping over said contacts, a spring for rotating said brushes, means comprising a toothed wheel and an electromagnetically controlled stopping pawl for stopping said brushes when they reach a designated set of contacts, a stopping member for stopping the brushes in their normal positions, a member for disengaging the stopping member from the brushes and for causing said brushes to be held in their normal positions by said stopping pawl alone, said disengaging member being arranged to move the. stopping member from its stopping position and to allow said stopping member to return to its stopping position in a periodv of time less than that required for the movement of said brushes from and back to their normal position. l

5. In a telephone system, calling lines, a plurality of finder switches adapted to be antomatically operated in response to the initiation of a call on one of said lines, said finders adapted to act in tandem relation in extending the calling line, a preselecting trunk finder switch associated with each of said line finders, means efiective when the line finder associated with a preselected trunk fails to reach the calling line within a given time interval to cause said trunk finder to start another line finder, said last mentioned means comprising a multi-position timing switch.

6. A telephone system according to claim 5 in which the timing switch also efiects an intermittent connection of ringing current to the called line.

7 In a telephone system, a calling line, a called line, a plurality of line finder switches adapted to act in tandem relation for extending the calling line, a step-by-step timing switch associated with said line finders for automatically starting a second line finder when a first line finder fails to reach the calling line within a predetermined interval, a ringing cut-oil and through connecting relay for completing connection between the calling and called lines, and means controlled by said timing switch for applying ringing current to the called line through the contacts of said relay.

8. A switch for automatic telephone systems having aself-contained power drive, a contact bank, a brush set cooperating with the said bank, said brushes adapted to travel in a continuous motion over said bank and means for positively arresting said brushes on any set of contacts comprising an electromagnetically operated armature, a detent carried by said armature and adjustable thereon, and means for adjusting said contact bank with respect to said brush set.

9. In a telephone system, a plurality of telephone lines, each line comprising talkingconductors and a test conductor, a plurality of coresponding bank contacts in which, said linesterminat'e, the test contacts having 

